The present invention relates to a semiconductor device and to a method of manufacture thereof; and, more particularly, the invention relates to a technique that is effective when applied to a semiconductor device which is formed by a method having a step of forming patterns by the so-called liftoff method.
There are, for example, semiconductor devices using a Group III-V compound of the periodic table, such as gallium arsenide (GaAs). Such compound semiconductors are characterized by the fact that they exhibit a greater mobility than Si (silicon), which enables preparation of semi-insulating crystals and liquid crystals, and a heterojunction can be formed by using them.
For example, a hetero-junction bipolar transistor (HBT) using gallium arsenide is formed as a bipolar transistor using GaAs as a base layer and a heterogeneous semiconductor, such as InGaP (indium gallium phosphide) or AlGaAs (aluminum gallium arsenide), as an emitter layer. It is possible to increase the a current amplification ratio and thereby improve the properties of a transistor by using a heterojunction (heterogeneous junction) to increase the forbidden band width of the emitter over that of the base in an emitter-base junction.
For example, Japanese Patent Application Laid-Open No. 2001-1898319 ([0034], FIG. 4) describes an HBT using GaAs as a base layer and InGaP as an emitter layer. In this device, the emitter contact layer (16) is formed as a substantially annular structure. In addition, the emitter electrode (17) is designed so that wiring does not need to cross over the emitter electrode (17) upon formation of an extraction interconnect of the base electrode (19).
Japanese Patent Application Laid-Open No. 2002-246587 ([0041], FIG. 17) discloses a GaAs type HBT whose base layer (3) and an emitter layer (4) have a circular planar shape.
Japanese Patent Application Laid-Open No. 2000-277530 (Summary, FIG. 1) discloses a GaAs type HBT. It has, on the back side of its substrate, a via hole and a metal film that is adhered on the back side of the substrate.